Residuum cracking in a pebble heater



1954 R. A. FINDLAY RESIDUUM CRACKING IN A PEBBLE HEATER Filed Sept. 11,1950 2a 3;; PRODUCT TO RECOVERY STEPS |I| ll 26 1 39 .l 19 27- J; l4 244 FLUE cAs x 42 LIFT cAs INVENTOR. R A. FINDLAY BY 7A A TTORNE Y5Patented Oct. 19, 1954 RESIDUUM CRACKING IN A PEBBLE HEATER Robert A.Findlay, Bartlesville, Okla. assignor to Phillips Petroleum Company, acorporation of Delaware Application September 11, 1950, Serial No.184,233

6 Claims. 1

This invention relates to cracking of heavy residual hydrocarbons in apebble heater.

Pebble heater type apparatus is finding increasing favor in effectingthe conversion of various types of hydrocarbon streams into moredesirable hydrocarbons, particularly hydrocarbon conversions involvingcracking and reforming. Typical pebble heater operation entails heatinga gravitating mass of refractory pebbles in an upper heating chamber bycontact with hot flue gas formed in the bottom of the chamber bycombustion of a light hydrocarbon fuel with air, gravitating theresulting hot stream of pebbles through a restricted pebble throat orpassageway into a lower chamber wherein the hot column of pebbles iscontacted in countercurrent flow with a stream of hydrocarbon vaporunder conversion conditions of temperature, time, and pressure. Thestream of pebbles emerges from the bottom of the reactor or furnaceconsider:- ably cooled and flows downwardly to the lower end of a pebbleelevator which elevates the pebbles to a chute leading into the upperpart of the pebble heating chamber through which they are delivered tobe reheated. In this manner heat is imparted to the refractory pebbleswhich are utilized to carry the heat for the process to the conversionchamber. In this type of operation as contrasted with hydrocarbonconversion in a regenerative furnace, the flue gas for the process isnot mixed with the hydrocarbon product and it is also possible tooperate continuously onstrean'l in the conversion of the hydrocarbon.

lhe term pebble as referred to throughout the specification includes anyparticulate refractory contact material of suitable form, size, anddensit to be readily flowable through the pebble heater chambers andcapable of withstanding temperatures upwards of 250 0 F. The pebbles arepreferably spherical and range from r; to 1" in diameter. Uniform shapesand sizes are preferred but pebbles of irregular shapes and sizes areoperable with less efficient results. Common materials utilized informing pebbles include alumina, mullite, zirconia, thoria, periclase,synthetic and natural clays, either alone or in combination with eachother.

For some time one of the problems of the petroleum industry has been toutilize the overabundance of heavy residual hydrocarbons resulting frompetroleum processing. It is this problem with which the invention isconcerned. a The principal object of the invention is to provide aprocess for converting heavy residual hydrocarbons to lighter, morevaluable hydrocar icons in which all of the heat requirements of theprocess are obtained from the residual hydrocarbon. It is also an objectof the invention to provide a method for removing entrained undesirabletars and carbonaceous constituents from a hot hydrocarbon eilluent so asto reduce and minimize formation of emulsions and coking troubles inlater separation and recovery steps. Another object is to provide aprocess which utilizes the least valuable fraction of a heavy residuum.A further object is to improve the efficiency of a process for theconversion of heavy hydrocarbons in a pebble heater. Other objects ofthe invention will become apparent from a consideration of theaccompanying disclosure.

In accordance with the invention, a heavy hydrocarbon residuum boilingat a temperature upwards of 500 F. is cracked by introducing the feed inliquid form into the upper section of a pebble heater reactor where itis contacted with a gravitating contiguous stream of hot pebbles at atemperature in the range of 1006 to 1700 F. The pebbles are heated in achamber, directly above the reactor. by burning oil the tar and cokedeposited on the pebbles with a stream of air introduced to the bottomof the chamber. The coke and tar referred to are deposited on thepebbles at least in part in the reactor, the balance being deposited onthe pebbles in a quench chamber positioned directly above the pebbleheating chamber just referred to. In this uppermost quench chamber thepebbles are contacted with the hydrocarbon effluent from the reactorunder conditions such that an amount of heavy tar and other heavyhydrocarbon material in the effluent hydrocarbon stream is deposited onthe pebbles which, taken with the coke deposited on the pebbles in thereactor, supplies the required heat for the pebble heating step whenburned off with air in the middle chamber of the system. In this mannerthe uppermost chamber acts as a quenching chamber for the hydrocarbonproduct stream, thereby recovering from this stream a substantialportion of thefuel requirements of the process as well as a considerableportion of the sensible heat of the product stream. The removal ofentrained heavy hydrocarbon from the product stream passing through thequench chamber is a distinct aid in the succeeding product separationsteps since it practically eliminates the formation of emulsions andcoking dimcultie's in the product separation equipment.

7 Temperature conditions in the quench chamher are controlled indirectlyby spraying water or passing steam into the bottom of the reactor so asto decrease the temperature of the outgoing pebbles to the range of 500to 800 F., this temperature being controlled by the amount of water orsteam introduced at this point. The pebbles enter the quench chamber ata temperature in this range or slightly below, due to unavoidable heatlosses in the elevator equipment, and by diverting a portion of thepebble stream directly into the pebble heating chamber it is relativelyeasy to control the quench zone temperature so as to deposit therequired amount of carbonaceous material on the pebbles which, takenwith the coke thereon, supplies the entire heat requirements of theprocess.

It has been found desirable to introduce steam 7 either with thehydrocarbon feed or separately into the top of the reactor so as toassist in vaporizing the feed and simultaneously reduce the cokeformation in the top of the reactor. The steam admitted to the bottom ofthe reactor not only functions to control outgoing pebble temperature,but also assists in flushing the pebble stream, thereby removing atleast a portion of the hydrocarbon therefrom.

' It has been found feasible to utilize inert gases and normally gaseoushydrocarbons as the coolant and flushing gas in the lower section of thereactor. Gases such as nitrogen, C0, C02, methane, ethane, and propaneare suitable for this purpose. When operating in the higher temperaturesof the cracking range utilized, the use of propane as a flushing gasresults in some conversion and reforming involving propane.

The heat required for the steam fed into the reactor both at the top andbottom is preferably obtained by means of a waste heat boiler throughwhich the flue gas from the pebble heating chamber is passed so as torecover available It has been found necessary to utilize a feed to theprocess which boils at a temperature of at least 5il0 F. in order tomake it possible to deposit sufiicient heavy carbonaceous materials onthe pebbles in the reactor and in the quenching chamber to furnish thefuel requirements of the process. With thistype of feed it is practicalto maintain combustion temperatures in the pebble heating chamber up toat least 2000 F. Since the temperature of the pebbles entering thereactor must be in the range of 1000 to 1700 F., this combustiontemperature is ample. The pebble circulation rate required for theprocess utilizing alumina or mullite pebbles ranges from 40 to 75 poundsper pound of oil fed to the process, depending upon the type of feed andother operating conditions.

' For a more complete comprehension of the invention, reference may behad to the drawing whichis a diagrammatic elevational view of onearrangement of apparatus for performing the invention. The apparatuscomprises a series of 3 vertically aligned interconnecting pebblechambers arranged for gravitational flow therethrough. Lowermost chamberII is a reaction chamber having a feed inlet line l2 terminating 4 in aspraying means for dispersing a liquid feed to the reactor. An inwardlyand downwardly sloping circumferential baflie I3 is positionedintermediate the ends of the reactor to provide a vapor space betweenthe baffle and the wall of the reactor with which efiluent line [4communicates for withdrawing reaction products. Lines l6 and I1communicate with the upper and lower ends of the reactor, repectively,for feeding steam to the upper end and a coolant and flushing gas to thelower end. A steam line I8 from waste heat boiler I9 connects with linesl6 and I1 for delivery of steam to the reactor. Line 2| connects withline H for delivery of water or other coolant and fluid flushingmaterial to the r reactor when it is desired to use such in preferenceto steam.

Intermediate chamber 22 functions as a pebble heating chamber to whichair is supplied through line 23 leading into the lower end of thechamber. Under high temperature conditions the air burns oh the coke andcarbonaceous material on the pebbles passing through the chamber forminghot combustion gas which passes upwardly through the chamber and istaken off through line 2-4.' Line 2 1 passes through waste heat boilerIt to supply the heat for the steam for the process.

Pebble chamber 26 functions as a product quenching chamber and collectstarry and other carbonaceous materials contained in the efiluent productgas. the cooler pebbles which carry this combustible material into thepebble heating chamber below. Effluent line Hi from reactor ll entersthe lower portion of the quenching chambercon- .necting with adistributing conduit 21 therein.

The quench product gas egresses from the quenching chamber through line28 passing to suitable product recovery apparatus. a Interconnectingthroats 3i and 32 serve pass pebbles in a compact stream from one pebblechamber to another. Pebble circulation through the system is controlledby pebble feeder 33 positioned in pebble efiiuent conduit 34 leadingfrom the bottom of reactor ll. Pebble feeder 33 may be any type ofconventional feeder which may be controlled to feed pebbles at anydesirable rate into gas lift 36 through which a suitable lifting gassuch as steam is constantly passed so as to elevate the pebbles fed intothe lift to a surge chamber 31 positioned at an elevation above chamber26 so that pebbles can be gravitated thereto through chute 38 and topebble heating chamber 22 through chute 39. A pebble feeder M in line 39functions under the controlof temperature controller 42 which is re blesfrom line 34 to surge chamber 31 is Within the scope of the invention.

Specific example A heavy fuel oil having an A. P. I. gravity of 15 isprocessed by the method of this invention in the apparatus shown in thedrawing. The

Thesematerials are deposited on' feed, at temperature of 100 F., isintroduced into the upper portion of the cracking zone concurrent withpebbles entering from the pebble heating zone at a temperature of 1150F. Re action products leave the reaction zone at a temperature of 1050F., and are passed to the quench zone where they contact a portion ofthe recirculated pebbles, which are at a temperature of 800 F. Vaporousproducts leaving the quench zone, at a temperature of 850 to 950 F.,comprise gaseous to high boiling liquid hydrocarbons in approximatelythe following proportions:

Product: Wt. percent Gas (C4 and lighter) 30.4 Gasoline (C5-400 F.) 21.0Gas oil MOO-900 F.) M. 22.5 Heavy oil (900-1150 F.) 26.1

Total 100.0

Higher boiling reaction products not carried out of the quench zone inthe vapor stream are condensed on the pebbles and carried into thecombustion, or pebble heating, zone. There these materials, togetherwith carbon deposited on the pebbles in the reaction zone, are burnedwith air to supply all of the heat required in the process. The carbondeposition amounts to from 16-1'7% of the feed.

The pebbles leaving the cracking zone are quenched by a Water spray to atemperature of 800 F., the resulting steam passing out of the chamberwith the hydrocarbon products. The pebbles are elevated to a surge zonewhere they are divided into two streams, about passing to the quenchzone, as described above, and the remainder directly to the pebbleheating zone.

In another arrangement of apparatus for effecting the process of theinvention, quench chamber 20 is positioned opposite heating chamber 22and reactor H so that a short product effluent line (line H) connectsreactor l I with quench chamber 26. This arrangement requires anelevator such as that shown in the drawing and an additional elevatordisposed so as to receive pebbles from the lower section of the quenchchamber and to deliver them to a chute leading into heating chamber 22or to a surge chamber similar to chamber 31 disposed at a level abovethe pebble inlet to chamber 22. This modification of the apparatus isadvantageous in that it shortens eflluent line H! but it entails morecomplicated and expensive pebble transfer.

The illustrative details set forth herein are not to be construed asimposing unnecessary limitations upon the invention, the scope of whichis set forth in the claims.

I claim:

1. A process for cracking a heavy residual hydrocarbon which comprisesgravitating a stream of hot refractory pebbles through a series ofseparate connecting zones comprising a pebble heating zone, a crackingzone, and a product quenching zone; introducing a stream of liquid heavyresidual hydrocarbon boiling at a temperature of at least 500 F. to theupper end of said cracking zone and contacting the hot pebbles in saidcracking zone in concurrent flow so as to raise same to a crackingtemperature in the range of 1000 to 1700 F. under conditions whicheffect cracking of said hydrocarbon and deposition of coke on saidpebbles; withdrawing an efiluent hydrocarbon stream of cracked productfrom an intermediate section of the pebble bed in said reaction zonebelow the level of feed introduction; contacting the pebble stream inthe lower section of said recation zone with a relatively cool gas so asto reduce the temperature of the outgoing pebbles to the range of 500 to850 F.; transferring a first portion of the pebbles from the bottom ofthe reaction zone to the top of said quenching zone; contacting thepebbles in said quenching zone in countercurrent flow with said effluenthydrocarbon stream from said reaction zone so as to quench said productstream and deposit heavy tarry constituents of said stream on saidpebbles in an amount which when burned in said pebble heating zone withsaid coke furnishes the entire heat for heating said pebbles;transferring pebbles from the bottom of said quenching zone to the topof said pebble heating zone; transferring a second portion of saidpebbles from the bottom of the reaction zone directly to said pebbleheating zone; burning off the tarry deposit and coke on the pebbles insaid pebble heating zone with a stream of air so as to heat said pebblesto said cracking temperature solely by the heat of combustion of saidtarry deposit and coke; and recovering the quenched product.

2. The process of claim 1 in which the proportion of pebbles passing tosaid quenching zone is regulated in response to variations intemperature from a predetermined temperature in said pebble heatingzone.

3. The process of claim 2 in which the propor-- tion of pebbles passingto the quenching zone is maintained in the range of 5 to 50 per cent ofthe amount circulated.

4. The process of claim 1 in which said relatively cool gas is steam.

5. The process of claim 1 in which said relatively cool gas is anormally gaseous hydrocarbon.

6. The process of claim 1 in which a fixed proportion of the pebblescirculated is passed through said quenching zone and the temperature ofthe efiiuent pebbles from the pebble heating zone is regulated bycontrolling the amount of excess air fed thereto.

References Cited in the file of this patent UNITED STATES PATENTS-Number Name Date 2,389,635 Ramseyer Nov. 27, 1945 2,432,503 Bergstrom eta1. Dec. 16, 1947 2,432,962 Bergstrom Dec. 16, 1947 2,439,730 HappelApr. 13, 1948 2,532,613 Dutcher Dec. 5, 1950

1. A PROCESS FOR CRACKING A HEAVY RESIDUAL HYDROCARBON WHICH COMPRISESGRAVITATING A STREAM OF HOT REFRACTORY PEBBLES THROUGH A SERIES OFSEPARATE CONNECTING ZONES COMPRISING A PEBBLE HEATING ZONE; A CRACKINGZONE, AND A PRODUCT QUENCHING ZONE; INTRODUCING A STREAM OF LIQUID HEAVYRESIDUAL HYDROCARBON BOILING AT A TEMPERATURE OF AT LEAST 500* F. TO THEUPPER END OF SAID CRACKING ZONE AND CONTACTING THE HOT PEBBLES IN SAIDCRACKING ZONE IN CONCURRENT FLOW SO AS TO RAISE SAME TO CRACKINGTEMPERATURE IN THE RANGE OF 1000 TO 1700* F. UNDER CONDITIONS WHICHEFFECT CRACKING OF SAID HYDROCARBON AND DEPOSITION OF COKE ON SAIDPEBBLES; WITHDRAWING AN EFFLUENT HYDROCARBON STREAM OF CRACKED PRODUCTFROM AN INTERMEDIATE SECTION OF THE PEBBLE BED IN SAID REACTION ZONEBELOW THE LEVEL OF FEED INTRODUCTION; CONTACTING THE PEBBLE STREAM INTHE LOWER SECTION OF SAID RECATION ZONE WITH A RELATIVELY COOL GAS SO ASTO REDUCE THE TEMPERATURE OF THE OUTGOING PEBBLES TO THE RANGE OF 500 TO850* F.; TRANSFERRING A FIRST PORTION OF THE PEBBLES FROM THE BOTTOM OFTHE REACTION ZONE TO THE TOP OF SAID QUENCHING ZONE; CONTACTING THEPEBBLES IN SAID QUENCHING ZONE IN COUNTERCURRENT FLOW WITH SAID EFFLUENTHYDROCARBON STREAM FROM SAID REACTION ZONE SO AS TO QUENCH SAID PRODUCTSTREAM AND DEPOSIT HEAVY TARRY CONSTITUENTS OF SAID STREAM ON SAIDPEBBLES IN AN AMOUNT WHICH WHEN BURNED IN SAID PEBBLE HEATING ZONE WITHSAID COKE FURNISHES THE ENTIRE HEAT FOR HEATING SAID PEBBLES;TRANSFERRING PEBBLES FROM THE BOTTOM OF SAID QUENCHING ZONE TO THE TOPOF SAID PEBBLE HEATING ZONE; TRANSFERRING A SECOND PORTION OF SAIDPEBBLES FROM THE BOTTOM THE REACTION ZONE DIRECTLY TO SAID PEBBLEHEATING ZONE; BURNING OFF THE TARRY DEPOSIT AND COKE ON THE PEBBLES INSAID PEBBLE HEATING ZONE WITH A STREAM OF AIR SO AS TO HEAT SAID PEBBLESTO SAID CRACKING TEMPERATURE SOLELY BY THE HEAT OF COMBUSTION OF SAIDTARRY DEPOSIT AND COKE; AND RECOVERING THE QUENCHED PRODUCT.